This invention relates to forming metallic components, and more specifically to hot stretch forming and creep forming of titanium and its alloys by application of supplemental heating during selected stages of the stretch-forming process.
Stretch forming is a well-known process used to form curved shapes in metallic components by pre-stretching a workpiece to its yield point while forming it over a die. This process is often used to make large aluminum and aluminum-alloy components, and has low tooling costs and excellent repeatability.
Titanium or titanium alloys are substituted for aluminum in certain components, especially those for aerospace applications. Reasons for doing so include titanium's higher strength-to weight ratio, higher ultimate strength, and better metallurgical compatibility with composite materials.
However, there are difficulties in stretch-forming titanium at ambient temperature because its yield point is very close to its ultimate tensile strength with a minimal percent elongation value. Therefore, titanium components are typically bump formed and machined from large billets, an expensive and time-consuming process. It is known to apply heat to titanium components during stretch-forming by electrically insulating the titanium component and then heating the component by passing current through the component, causing resistance heating. However, there are applications where this process is not sufficient to achieve the desired result.
Accordingly, there is a need for an apparatus and method for stretch-forming titanium and its alloys. It has been determined that application of radiant heat to the component by means of proximate resistance elements provides further enhancement to the titanium-forming process.